<template>
	<view class="u-wrap">
		<view class="header">
			<view class="header-search" @click="$router.push('/pages/category/search/search')">
				<u-search inputAlign="center" height="40" shape="square" :showAction="false" placeholder="搜索商品,共1000件商品"
					class="search"></u-search>
			</view>
		</view>
		<view class="u-menu-wrap">
			<scroll-view scroll-y scroll-with-animation class="u-tab-view menu-scroll-view" :scroll-top="scrollTop"
				:scroll-into-view="itemId">
				<view v-for="(item,index) in tabbar" :key="index" class="u-tab-item"
					:class="[current == index ? 'u-tab-item-active' : '']" @tap.stop="swichMenu(index)">
					<text class="u-line-1">{{item.cate_name}}</text>
				</view>
			</scroll-view>
			<scroll-view :scroll-top="scrollRightTop" scroll-y scroll-with-animation class="right-box"
				@scroll="rightScroll">
				<view class="page-view">
					<view class="class-item" :id="'item' + index" v-for="(item , index) in tabbar" :key="index">
						<u-divider textColor="#000" class="item-title" :text="item.cate_name"></u-divider>
						<view class="item-container">
							<view class="thumb-box" v-for="(item1, index1) in item.children" :key="index1"
								@click="featureC(item1)">
								<image v-if="item1.icon != ''" class="item-menu-image" :src="item1.pic" mode=""></image>
								<view v-else class="item-menu-image row-c" style="background-color: #F4F6F8;"><text
										style="font-size: 20rpx;color: #d0d0d0;">加载失败</text></view>
								<view class="item-menu-name">{{item1.cate_name}}</view>
							</view>
						</view>
					</view>
				</view>
			</scroll-view>
		</view>
	</view>
</template>

<script>
	import { category } from '@/api/'

	export default {
		data() {
			return {
				scrollTop: 0, //tab标题的滚动条位置
				oldScrollTop: 0, // tab标题的滚动条旧位置
				current: 0, // 预设当前项的值
				menuHeight: 0, // 左边菜单的高度
				menuItemHeight: 0, // 左边菜单item的高度
				itemId: '', // 栏目右边scroll-view用于滚动的id
				tabbar: [], // 渲染的数据，放在最后供你们测试
				arr: [], // 储存距离顶部高度的数组
				scrollRightTop: 0, // 右边栏目scroll-view的滚动条高度
				timer: null // 定时器
			}
		},
		onReady() {
			this.load_cate();
			this.getMenuItemTop();
		},
		methods: {
			async load_cate() {
				let { status, data } = await category.cate();
				if (status === 200) {
					this.tabbar = [...data];
					console.log(data);
				}
			},
			getElRect(elClass, dataVal) {
				new Promise((resolve, reject) => {
					const query = uni.createSelectorQuery().in(this);
					query.select('.' + elClass).fields({
						size: true
					}, res => {
						// 如果节点尚未生成，res值为null，循环调用执行
						if (!res) {
							setTimeout(() => {
								this.getElRect(elClass);
							}, 10);
							return;
						}
						this[dataVal] = res.height;
						resolve();
					}).exec();
				})
			},
			/**
			 * 获取右边菜单每个item到顶部的距离
			 * 储存到 arr 数组里面用于后面滚动判断
			 */
			//forEach
			getMenuItemTop() {
				new Promise(resolve => {
					let selectorQuery = uni.createSelectorQuery();
					selectorQuery.selectAll('.class-item').boundingClientRect((rects) => {
						// 如果节点尚未生成，rects值为[](因为用selectAll，所以返回的是数组)，循环调用执行
						if (!rects.length) {
							setTimeout(() => {
								this.getMenuItemTop();
							}, 10);
							return;
						}
						rects.forEach((rect) => {
							// 视情况而定，这里减去rects[0].top，是因为第一项顶部可能不是贴到导航栏(比如有个搜索框的情况)
							// this.arr.push(rect.top - rects[0].top);
							this.arr.push(rect.top)
							resolve();
						})
					}).exec()
				})
			},
			/**
			 * 观测元素相交状态
			 * 检测右边scroll-view的id为itemxx的元素与right-box的相交状态
			 * 如果跟.right-box底部相交，就动态设置左边栏目的活动状态
			 */
			async observer() {
				this.tabbar.map((val, index) => {
					let observer = uni.createIntersectionObserver(this);
					observer.relativeTo('.right-box', {
						top: 0
					}).observe('#item' + index, res => {
						if (res.intersectionRatio > 0) {
							let id = res.id.substring(4);
							this.leftMenuStatus(id);
						}
					})
				})
			},
			/**
			 * 设置左边菜单的滚动状态
			 * @index 传入的 ID
			 */
			async leftMenuStatus(index) {
				this.current = index;
				// 如果为0，意味着尚未初始化
				if (this.menuHeight == 0 || this.menuItemHeight == 0) {
					await this.getElRect('menu-scroll-view', 'menuHeight');
					await this.getElRect('u-tab-item', 'menuItemHeight');
				}
				// 将菜单活动item垂直居中
				this.scrollTop = index * this.menuItemHeight + this.menuItemHeight / 2 - this.menuHeight / 2;
			},
			/**
			 * 点击左边的栏目切换
			 * @index 传入的 ID
			 */
			async swichMenu(index) {
				if (this.arr.length == 0) {
					await this.getMenuItemTop();
				}
				if (index == this.current) return;
				this.scrollRightTop = this.oldScrollTop;
				this.$nextTick(function() {
					this.scrollRightTop = this.arr[index];
					this.current = index;
					this.leftMenuStatus(index);
				})
			},
			/**
			 * 右边菜单滚动
			 * 如果不存在height2，意味着数据循环已经到了最后一个，设置左边菜单为最后一项即可
			 */
			async rightScroll(e) {
				this.oldScrollTop = e.detail.scrollTop;
				if (this.arr.length == 0) {
					await this.getMenuItemTop();
				}
				if (this.timer) return;
				if (!this.menuHeight) {
					await this.getElRect('menu-scroll-view', 'menuHeight');
				}
				setTimeout(() => { // 节流
					this.timer = null;
					// scrollHeight为右边菜单垂直中点位置
					// let scrollHeight = e.detail.scrollTop + this.menuHeight / 2;
					// scrollHeight为右边菜单头部位置
					let scrollHeight = e.detail.scrollTop + 20;
					for (let i = 0; i < this.arr.length; i++) {
						let height1 = this.arr[i];
						let height2 = this.arr[i + 1];
						if (!height2 || scrollHeight >= height1 && scrollHeight < height2) {
							this.leftMenuStatus(i);
							return;
						}
					}
				}, 10)
			},
			featureC(item) {
				console.log(item);
			}
		}
	}
</script>

<style lang="scss">
	.u-wrap {
		/* #ifdef H5 */
		height: calc(100vh - var(--window-top));
		/* #endif */
		display: flex;
		flex-direction: column;
		height: 100vh;
	}

	.header {
		padding: 10px;
		background-color: #fbfbfb;
		border-bottom: 1px solid #ddd;
	}

	.header-search {
		margin: 0 auto;
		width: 95%;
	}



	.u-search-box {
		padding: 18rpx 30rpx;
	}

	.u-menu-wrap {
		flex: 1;
		display: flex;
		overflow: hidden;
	}

	.u-tab-view {
		width: 200rpx;
		height: 100%;
		background-color: #f6f6f6;
	}

	.u-tab-item {
		height: 110rpx;
		background: #f6f6f6;
		box-sizing: border-box;
		display: flex;
		align-items: center;
		justify-content: center;
		font-size: 26rpx;
		color: #444;
		font-weight: 400;
		line-height: 1;
	}

	.u-tab-item-active {
		position: relative;
		color: red;
		font-size: 30rpx;
		font-weight: 500;
		background: #fff;
	}

	.u-tab-item-active::before {
		content: "";
		position: absolute;
		border-left: 5rpx solid #f96c29;
		height: 100%;
		left: 0;
		top: 0;
	}

	.u-tab-view {
		height: 100%;
	}

	.right-box {
		background-color: #fff;
	}

	.page-view {
		padding: 16rpx;
	}

	.class-item {
		margin-bottom: 30rpx;
		background-color: #fff;
		padding: 16rpx;
		border-radius: 8rpx;
	}

	.class-item:last-child {
		min-height: 100vh;
	}

	.item-title {
		font-size: 26rpx;
		text-align: center;
		font-weight: bold;
	}

	.item-menu-name {
		margin-top: 8rpx;
		font-weight: normal;
		font-size: 24rpx;
		color: #444;
	}

	.item-container {
		display: flex;
		flex-wrap: wrap;
	}

	.thumb-box {
		width: 33.333333%;
		display: flex;
		align-items: center;
		justify-content: center;
		flex-direction: column;
		margin-top: 20rpx;
	}

	.item-menu-image {
		width: 120rpx;
		height: 120rpx;
	}
</style>